(1) Field of the Invention
One of the problems encountered when a laser system is designed and intended for use in an industrial environment is the compactness, size and reliability of the system. Lasing action in a system is obtained by subjecting a gas-filled vessel or channel to an electric discharge to form plasma; the electrons provided by the discharge collide with active gas molecules thereby exciting them to higher energy levels, from which they descent to lower energy levels and emit excess energy in the form of photons, or light quanta. The density of particles in the higher energy level must exceed that in the lower energy level to achieve optical gain. The addition of oxygen, water vapor, hydrogen and helium to a mixture of carbon dioxide and nitrogen has been found to yield increased output.
An electrical discharge having a large cross sectional area which will uniformly fill large volume cavities regardless of size or shape is mandatory if powerful and reliable lasers suitable for industrial applications are to be developed. An electrical discharge is normally very restricted in diameter because the temperature in different parts of the discharge is not uniform and this results in lower density and higher current at the inside of the plasma column, thus constricting the column. Ballasting the electrodes offers a partial solution by spreading the emission, but the streams tend to recombine. Judicious use and design of aerodynamic forces to control the ion and electron distribution in a large volume discharge have achieved some success and have resulted in a degree of compactness and reduction in size for the same power output, as measured against the very long discharge systems known in the prior art.
(2) Description of the Prior Art
Commercial application of lasers has been limited in the past because of the limitations of poor reliability, poor beam quality and large size and heavy weight. These problems, coupled with the high cost of lasers per watt of output, have caused the machine tool industry and other industries which can use lasers to proceed very slowly in their use. As an example of the size and weight problem, current high power (1 kw and up), continuous wave lasers measure about 22 feet long by 7 feet wide by 5.5 feet high and weigh several tons.
This invention is directed toward solving this problem. It leads to lower manufacturing costs and lower cost per watt of output. The laser embodied herein has high reliability and exceptional beam quality at high power and reduced size and weight.
Lasers are used to reduce production costs in those applications requiring cutting, welding, drilling, heat treating and other processes. However, according to industry publications, laser sales are only about three percent of the machine tool industry. Use of this invention's improved reliability will enable industry to put lasers on industrial production lines. Improved beam quality will make possible industry applications such as hardening or softening metals or adhering materials to one another, which previously could not be economically done. Miniaturization of the structure opens robotics applications, and eventual lower costs will mean more industries can replace other equipment with lasers.
A significant step forward in controlling the ion and electron distribution in an industrial laser discharge to thereby realize large volume uniform plasma generation and control has been achieved according to this invention by pumping a primary lasing gas stream in a recirculating mode in the path of a plurality of spaced high voltage discharges, and introducing a secondary lasing gas stream through a plurality of ejectors into the primary lasing gas stream, thereby effecting turbulance and diffusion of the gas streams, a pressure rise equal to the recirculating mode pressure drop, and an increase in mass flow. Thus the large pump previously needed for state of the art lasers is sharply reduced in size, weight, and capacity, leading to higher system efficiency, lower cost, and lower input energy requirements. It has been found that an exceptional and unusual characteristic of the ejector contributes significantly to the turbulance and diffusion of the lasing gas streams. As the high velocity gas secondary gas stream emerges from the ejector nozzle it enters a mixing tube of generally cylindrical form and the gas from the primary recirculating stream is thus entrained by massive collisions between gas molecules. Vortices result from the collisions and these vortices blend the several streams homogeneously. The angular velocities of the vortices diminish as the blended gases progress downstream. An aerodynamic contour is formed at the exit area of the mixing tube to develop a radial component of flow to the blended gas streams. This yields an homogeneous longitudinal flow in the laser channel with uniform radial velocity distribution.
In the initial reduction to practice of the 5 kw laser structure to be hereinafter described it has been found that the level of plasma control obtained removes constraints on the laser geometry so that large volume cavities can be uniformly filled with plasma, and one can thus design an optimum optical system. The very large and sturdy optical mirrors which can now be used result in a lower flux density and thus prevent warping and destruction from heat. The technology eliminates the necessity for the very delicate, fragile, and expensive optical systems which are not necessarily adaptable to industrial use.
It is expected that the use of plasma control to uniformly fill a large volume cavity will yield a 5 kw laser having dimensions of approximately two feet by two feet by one foot, thus enabling industry to use the laser on a robot arm.